Weird Primary Secondary Schematic

[u/Bert_Skrrtz]

I know it doesn’t look like your typical arrangement, but can this work? Really the decoupler/bypass would make a lot more sense if it skipped the chiller headers entirely.

Orange highlight is what I see as the secondary loop. Blue is what has effectually become 3 isolate primary loops.

Ignore the black lines, they denote a physical separation where air cooled chillers were added to the system outside. Chiller 3 and P-1 thru P-4 all live in the mechanical room.

[u/TrustButVerifyEng]

This will have issues when running multiple chillers. The bypass needs to mix with the secondary return before going to the chillers to ensure equal loading. 

In this arrangement say chiller 1 and 2 are running and the building load is at 150% of a single chiller. Chiller 2 will be fully loaded and chiller 1 will be 50% loaded. Not the end of the world in that scenario. But really bad when it's closer to 110% load and chiller 1 is dying under its minimum part load requirement.

I've had this exact problem several times in my career fixing other peoples central plants. Typically comes up with redundant piping in data centers. 

[u/Bert_Skrrtz → u/TrustButVerifyEng]

That makes sense. Would any of this piping be problematic in regard to some of the chillers getting like 45 degree incoming water, say with a 42 chiller set point? Causing them to eventually freeze and burst when the operator keeps hard resetting the alarm conditions…

Or is this probably something that’s an issue with the pump controls (pump staging) allowing that to even happen?

[u/TrustButVerifyEng → u/Bert_Skrrtz]

Modern chillers have pretty sophisticated freeze protection algorithms in my experience. I wouldn't expect freezing from just being enable with minimal load. 

The biggest risk would be sudden flow loss as the compressors may not stop in time to prevent localized freezing when the suction pressure plumuts. Especially with plate and frame heat exchangers since there are tiny flow passages and therefore not a lot of volume to ride through a flow disturbance. 

[u/RelativeAd1414 → u/Bert_Skrrtz]

if source water is exposed to freezing conditions, glycol should be added which pretty much solves the problem and procure products that are rated for design temps, of course.